A PCR assay used to study aerosol transmission of Actinobacillus pleuropneumoniae from samples of live pigs under experimental conditions

The study describes a polymerase chain reaction (PCR) assay for the detecti on of Actinobacillus pleuropneumoniae. The test is based on the amplificati on of the omlA gene coding for an outer membrane protein of A. pleuropneumo niae. To test the specificity of the reaction, 19 other bacterial species r elated to A. pleuropneumoniae or isolated from pigs were assayed. They were all found negative in the PCR assay, The detection threshold of the test w as 10(2) A. pleuropneumoniae CFU/assay. The test was then applied to the de tection of A. pleuropneumoniae from tonsillar biopsies and tracheobronchial lavage fluids of pigs without a culture step. The detection of A. pleuropn eumoniae in these samples was performed by PCR, by conventional culture and by bacteriology with immunomagnetic beads. The number of samples that were found positive by PCR was almost three times higher than the number of sam ples from which A. pleuropneumoniae was isolated by both bacteriological te chniques. The detection of A. pleuropneumoniae in these samples allowed us to demonstrate its aerosol transmission to pigs under experimental conditio ns. The trial involved 18 specific pathogen free pigs. Six pigs, infected w ith A, pleuropneumoniae, were located in a unit A, together with four non-i nfected animals (contact pigs). Eight non-infected pigs (reporter pigs) wer e located in a unit B, adjacent to A. We detected A. pleuropneumoniae in sa mples from infected animals but also from 'contact' (unit A) and 'reporter' (unit B) pigs. The results of this study show that the simple preparation of the samples followed by the PCR assay may be a useful tool for epidemiol ogical studies. (C) 2000 Elsevier Science B.V. All rights reserved.